perl - What is 4/16 in hashes?

Question

if (%hash){
     print "That was a true value!
";
}

That will be true if (and only if) the hash has at least one key-value pair.

The actual result is an internal debugging string useful to the people who maintain Perl. It looks something like "4/16," but the value is guaranteed to be true when the hash is nonempty, and false when it's empty. --Llama book

What is this 4/16? Can anyone show me a small program from where I can see that the result is 4/16?

Answer 1

From perldoc perldata:

If you evaluate a hash in scalar context, it returns false if the hash is empty. If there are any key/value pairs, it returns true; more precisely, the value returned is a string consisting of the number of used buckets and the number of allocated buckets, separated by a slash. This is pretty much useful only to find out whether Perl's internal hashing algorithm is performing poorly on your data set. For example, you stick 10,000 things in a hash, but evaluating %HASH in scalar context reveals "1/16" , which means only one out of sixteen buckets has been touched, and presumably contains all 10,000 of your items.

so, 4/16 would be the buckets used/allocated count, and something like the following will display this value:

%hash = (1, 2);
print scalar(%hash); #prints 1/8 here